The present invention relates to web drying apparatus. In drying a moving web of material, such as paper, film or other sheet or planar material, it is often desirable that the web be dried quickly, and that the length of the dryer be limited in view of space and cost constraints. Various attempts have been made in the prior art for decreasing the length and/or increasing the efficiency and line speed of web dryers. To that end, infrared radiation has been used either alone or in combination with air to dry the web. For example, U.S. Pat. No. 4,936,025 discloses a method for drying a moving web by passing the web free of contact through various drying gaps. Thus, the web is passed through an infrared treatment gap in which infrared radiation is applied to the web from an infrared unit, and then is passed into an air-drying gap within which the web is dried by gas blowings from an airborne web dryer unit which simultaneously supports the web free of contact. Further, U.S. Pat. No. 4,756,091 discloses a hybrid gas-heated air and infrared radiation drying oven in which strips of infrared heaters are arranged with heated air inflow nozzles alongside thereof. U.S. Pat. No. 5,261,166 discloses a combination infrared and air flotation dryer wherein a plurality of air bars are mounted above and below the web for contactless convection drying of the web, and a plurality of infrared gas fired burners are mounted between air bars.
In many conventional infrared dryers, however, much of the heat supplied by the infrared energy source is lost to surroundings by transmission, reflection and radiation. In addition, the infrared elements must be continually turned on and off to avoid burning of the web. This reduces efficiency and can reduce infrared element life. Also, if dryer atmosphere with high solvent concentrations comes into contact with the hot infrared heating elements, explosion could result.
It is therefore an object of the present invention to provide a more efficient combination infrared/air flotation dryer for drying moving webs.
It is a further object of the present invention to provide optimal control of an infrared/air flotation dryer.
It is a still further object of the present invention to provide infrared and air drying while floatingly supporting the moving web.
It is another object of the present invention to eliminate the need to continually turn the infrared elements on and off during the drying operation without sacrificing safety.
It is a further object of the present invention to prevent a potentially explosive dryer atmosphere from contacting the high temperature heating surface in the dryer.